1. Field of the Invention
The present invention relates to a valve drive system for an internal combustion engine and a method corresponding to the operation of the same system.
2. Description of the Related Art
A known electromagnetic valve mechanism incorporated in an internal combustion engine includes electromagnetic valves each having at least one magnet and a pair of springs as its main components (see JP-A 59-213913). Typically, such springs are arranged so as to hold each valve in its default state at the center between one end of the valve moving range at which the valve is fully open (will hereinafter be referred to as “fully open position” where appropriate) and another end at which the valve is fully closed (will hereinafter be referred to as “fully closed position” where appropriate). Setting the default valve position at such a middle position offers an advantage that less power is required to open, close, and hold the valve. With this arrangement, if current applied to the magnet holding the valve at the fully open or closed position is shut off, the valve then starts oscillating on its own due to the urging force of each spring. Hereinafter, such oscillation of each valve will be called “free oscillation.”
When the valve is thus oscillating, it causes some noise (will be called “off-valve noise”). Thus, the related art mechanism described above involves a problem that it will be very noisy if such off-valve noise is simultaneously generated from a number of valves in an internal combustion engine having a plurality of cylinders.
Another electromagnetic valve system is known in which a valve is held at a fully closed position in its default state (see JP-A 2000-161032). However, such a system typically requires a complicated structure enabling the valve to be held at such an open position. Therefore, it is desirable to accomplish reduction of off-valve noise with an ordinary electromagnetic valve system.